If an extraterrestrial civilization were trying to detect human signals, where and when would they be most likely to find them? A recent study by researchers at Penn State and NASA’s Jet Propulsion Laboratory in Southern California examined the timing and directions of deep space transmissions from Earth. They found patterns that could not only reveal how outsiders might detect us but also help refine our own strategies in the search for extraterrestrial intelligence (SETI).
“Humans are predominantly communicating with the spacecraft and probes we have sent to study other planets like Mars,” said Pinchen Fan, graduate student in astronomy and astrophysics in the Penn State Eberly College of Science, science principal investigator of the NASA grant supporting this research and first author of the paper. “But a planet like Mars does not block the entire transmission, so a distant spacecraft or planet positioned along the path of these interplanetary communications could potentially detect the spillover; that would occur when Earth and another solar system planet align from their perspective. This suggests that we should look for alignment of planets outside of our solar system when searching for extraterrestrial communications.”
The team’s paper was published on Aug 21, 2025, in Astrophysical Journal Letters, with findings also presented that same day at the Penn State SETI Symposium, hosted by the Penn State Extraterrestrial Intelligence Center.
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